IGBT assembly having circuitry for injecting/extracting current into/from an auxiliary P well

ABSTRACT

An IGBT die structure includes an auxiliary P well region. A terminal, that is not connected to any other IGBT terminal, is coupled to the auxiliary P well region. To accelerate IGBT turn on, a current is injected into the terminal during the turn on time. The injected current causes charge carriers to be injected into the N drift layer of the IGBT, thereby reducing turn on time. To accelerate IGBT turn off, charge carriers are removed from the N drift layer by drawing current out of the terminal. To reduce V CE(SAT) , current can also be injected into the terminal during IGBT on time. An IGBT assembly involves the IGBT die structure and an associated current injection/extraction circuit. As appropriate, the circuit injects or extracts current from the terminal depending on whether the IGBT is in a turn on time or is in a turn off time.

TECHNICAL FIELD

The described embodiments relate to Insulated Gate Bipolar Transistors(IGBTs).

BACKGROUND INFORMATION

FIG. 1 (Prior Art) is a symbol of an N-channel enhancement typeInsulated Gate Bipolar Transistor (IGBT). There are several symbols inuse for such an IGBT. FIG. 1 is but one of these symbols. Whereas in apower field effect transistor structure the current flow between drainand source is due primarily to the flow of majority carriers, in an IGBTstructure the current flow between collector and emitter is due both tomajority carrier flow and to minority carrier flow. Accordingly, for agiven semiconductor die area, an IGBT can generally switch a largercurrent than a power field effect transistor of the same semiconductordie area. IGBTs are therefore preferable for certain applications. TheIGBT symbol 1 includes a gate terminal 2, an emitter terminal 3, and acollector terminal 4.

FIG. 2 (Prior Art) is a simplified cross-sectional diagram of an IGBT.Epitaxial layers 6 and 7 are grown on a P++ type substrate layer 5. N+type buffer layer 6 is disposed on the P++ type substrate layer 5. N−type drift layer 7 is disposed on the N+ type buffer layer 6. A P typebody region 8 extends down into the N− type drift layer 7, and an N+type source region 9 extends down into the P body region 8. There areseveral different topologies for an IGBT. The IGBT of FIG. 2 is one ofthese topologies. The P type body region shown on the left in thecross-section of the particular topology of FIG. 2 is part of the P typebody region 8 on the right. A gate 10, such as a gate of polysiliconmaterial, is separated from the planar upper semiconductor surface by athin gate insulation layer 11. An emitter metal terminal 12 straps eachP type body region to its corresponding N+ type source region as shown.A collector metal terminal 13 is disposed on the bottom side of the P++type substrate layer 5. A gate terminal (not shown) is provided to makecontact with the gate.

The IGBT can be considered to have a field effect transistor portion anda bipolar transistor portion. If the voltage V_(CE) between thecollector and the emitter is negative, then the P++ substrate to N−drift junction is reverse biased. Due the reverse biasing of thisjunction, there is no current flow between the collector and emitter.The IGBT is off and nonconductive. This condition is referred to as the“reverse blocking mode”. The term “reverse” is due to the P++ substrateto N− drift junction being reverse biased.

If the collector-to-emitter voltage V_(CE) is positive, and if thevoltage V_(GE) between the gate and the emitter is less than a thresholdvoltage V_(TH) (for example, V_(GE) is zero volts), then there is alsono current flow between the collector and emitter. Due to the V_(GE)being less than the threshold voltage V_(TH) there is no conductivechannel through the P type body region between the N+ type source region9 and the N− type drift layer 7. Electrons cannot flow from the N+ typesource region 9, through a conductive channel, and to the N− type driftlayer, and on to the collector. Consequently there is no current flowbetween the collector and emitter. This condition is referred to as the“forward blocking mode”.

If the collector-to-emitter voltage V_(CE) is positive, and if thevoltage V_(GE) between the gate and the emitter is initially less thanthe threshold voltage V_(TH) but is then raised to be greater than thethreshold voltage V_(TH) (for example, V_(GE) is raised to fifteenvolts), then a thin layer of the P type body region under the gate atthe upper surface of the semiconductor material inverts and becomes aconductive channel. Under the influence of a positivecollector-to-emitter voltage V_(CE), electrons flow from N+ type sourceregion 9, laterally through the conductive channel and across the P typebody region, and to the portion of the N-type drift layer 7 under gate10. Some of these electrons recombine with holes in the N-drift layer,but others continue downward through the N− type drift layer 7 anddownward through the N+ buffer layer 6. The current flow passes throughthe P++ type substrate layer 5 and to the collector terminal 13. Arrows14 and 15 indicate paths of these electrons into the N− type drift layer7. The flow of electrons into the N− type drift layer 7 increases theconcentration of electrons in the N− type drift layer 7, therebyreducing the potential of N− type drift layer 7. The reduced potentialon the N− type drift layer 7 causes the PN junction between the P++ typesubstrate 5 and the N+ type buffer layer 6 to be more forward biases.Holes are therefore emitted from the P++ type substrate layer 5 into theN+ type buffer layer 5. These holes pass upward through N+ type driftlayer 6. The holes that do not recombine with electrons in the N− typedrift layer 7 pass through N− type drift layer 7, and enter P type bodyregion 8. The holes do not flow into N+ type source region 9 so theypass under N+ type source region 9 and around the N+ type source region,and then upward to emitter terminal 12. Arrow 16 in FIG. 2 indicates apath of this hole current. The emission of holes from the P++ typesubstrate layer 5 into the N+ buffer layer 6 and into the N− type driftlayer 7 also causes the concentration of holes in the N− type driftlayer 7 to increase. This increase of the hole concentration in the N−type drift layer 7 causes more electrons to be drawn through the channelfrom the N+ type source region 9. The electrons are drawn through thechannel and into the N− type drift layer 7 in an attempt to equalizecharge in the N-type drift layer 7. A high density electron/hole “gas”exists in the N− type drift layer 7. Current flow between the emitterterminal and the collector terminal is therefor due both to electronflow into the N− type drift layer 7 as well as to hole flow into the N−type drift layer 7. Substantial collector-to-emitter current flows. Thiscondition is referred to as the “forward conduction mode”.

To turn the IGBT on, an amount of time is required for the high densityelectron/hole “gas” to be established in the N− type drift layer 7 bythe processes described above. Similarly, for the IGBT to be turned off,an amount of time is required for the holes and the electrons of thehigh density electron/hole “gas” to be removed from the N− type driftlayer 7 or for the holes and electrons of the “gas” to recombine.

Such an IGBT may, however, be susceptible to a phenomenon referred to aslatchup. During normal operation in the forward conduction mode asexplained above, the channel is conductive and electrons flow from theN+ source region 9, through the channel, to the N− type material underthe gate, then down through the N− type drift layer 7 to the P++ typesubstrate 5. As explained above, this causes a flow of holes upward fromthe P++ type substrate 5, up through the N− type drift layer 7, and thenlaterally through the P type body region 9 under the N+ type sourceregion 9, and to the emitter terminal 12. The electrons flowing from theN− type drift layer to the P++ type substrate is actually abase-to-emitter current of a PNP transistor, where the emitter of thePNP transistor is the P++ type substrate layer 5, where the base of thePNP transistor is the N-type drift layer 7 and the N+ type buffer layer6, and where the collector of the PNP transistor is the P type bodyregion 8. This PNP transistor is therefore on and conductive duringnormal operation in the forward conduction mode. In normal operation inthe forward conduction mode, however, the IGBT can be turned off usingthe gate by stopping electron flow through the channel. Stoppingelectron flow through the channel eliminates the base current of the PNPtransistor and turns the PNP transistor off.

In a latchup situation, however, the flow of holes passing laterallyunder the N+ type source region 9 is large. The P type body materialthrough which these holes flow when they pass laterally under the N+type source region 9 has a resistance. This resistance is indicated inFIG. 2 by the resistor symbol 17. If the flow of holes through thisresistance 17 is great enough, then the voltage on a part of the P typebody region 8 will rise with respect to the voltage on emitter terminal12 and N+ type source region 9. This portion of the P type body region 8that experiences the rise in voltage happens to be the base of aparasitic NPN transistor, where the N+ type material of the sourceregion 9 is the emitter of the parasitic NPN transistor, and where theN− type drift layer 7 is the collector of the parasitic NPN transistor.The rise in voltage on the base of the parasitic NPN transistor due tohole flow is a base current and turns the parasitic NPN transistor on.The parasitic NPN transistor turns on and provides a second source ofbase current to the PNP transistor. The PNP transistor cannot then beturned off by the gate cutting electron flow through the channel becausethere is now a second source of base current for the PNP transistorthrough the parasitic NPN transistor. The PNP transistor thereforeremains on regardless of the voltage on the gate. The PNP transistor inturn continues to supply holes that pass up into the P type body 8, andthat then flow laterally under the N+ type source region 9, acrossresistance 17, and keep the parasitic NPN transistor turned on. The twotransistors therefore keep each other turned on. This condition isreferred to as latchup. Latchup can cause very large localized currentsthat can destroy an IGBT.

FIG. 3 (Prior Art) is a simplified cross-sectional diagram of an oldIGBT structure that was sometimes employed in the past. A P type wellregion 18 referred to as a hole “diverter” was provided. In differentimplementations, this bottom of the diverter had different topologies.In some prior art designs, a PN diode diverter had a dynamic clampingbehavior. In the example of FIG. 3, the diverter 18 has a bottomboundary topology that is similar to the topology of the bottom of Pbody region 8. When the IGBT is turned on in the forward conductionmode, electrons flow from the N+ source region 9, through the conductivechannel, down through the N− type drift layer 7, and downward asdescribed above. Similarly, as described above, holes are emitted fromthe P++ type substrate layer 5 and flow up to the P body region 8. Inthe structure of FIG. 3, however, some of these holes that are passingupward through N− type drift layer 7 are “diverted” to the left and flowinto the P type diverter 18. Arrow 19 illustrates the path of thesediverted holes. The diverted holes cause a current to flow from thediverter 18 and to the emitter terminal 12, but the diverted holesreduce the magnitude of hole current flowing under the N+ type sourceregion 9. By diverting holes and reducing the magnitude of hole flow 16through the resistance 17, the voltage rise on the base of the parasiticNPN transistor is reduced. Reducing the rise in the voltage on the baseof the parasitic NPN transistor prevents the parasitic NPN transistorfrom turning on, and prevents latchup. The P type diverter 18 is coupledvia emitter terminal 12 to P type body region 8 as shown so that if thevoltage on a localized part of the P type body region were to start torise due to a large lateral hole flow through resistance 17, then moreholes would be diverted to the relatively lower voltage of the nearbydiverter 18. The diverter structure may have reduced the susceptibilityof the IGBT to latchup, but the presence of the diverters caused theV_(CE(SAT)) of the IGBT to be larger. Having a low V_(CE(SAT)) is a veryimportant quality of an IGBT in many applications. The diverterstructure of the past is therefore seldom if ever seen in commercialIGBTs.

In contemporary IGBTs, various techniques are employed to preventlatchup. FIG. 4 (Prior Art) is a diagram of an IGBT that is designedusing some of these techniques. The contour of the P type body region toN− drift layer is different as compared to the P type body to N− typedrift boundary of many prior IGBTs, and the doping profile within the Ptype body region is tailored by careful control of dopant implanting,such that some of the holes flowing up from the P++ type substrate inthe forward conduction mode enter the P-body region at a lower locationon the P type body to N− type drift boundary. Arrow 20 in FIG. 4illustrates this diverted current flow. This diverted current flowreduces the amount of current that flows through resistance 17 directlyunder the N+ source region. The hole current is spread out in the P typematerial of the P type body region. Moreover, the resistivity of atleast some of the P type material through which the hole current flowsin the deeper parts of the P type body region is made to be lower thanthe resistivity of the P type material directly underneath the N+ typesource. In some prior art devices, a floating P well is provided. This Pwell is floating and is not connected to any terminal. The floating Pwell serves to increase breakdown voltage of the IGBT. Due to acombination of all these factors and techniques, in contemporary IGBTstructures there is no localized voltage drop in the P type body regionsufficient to turn on the NPN parasitic transistor. Latchup is thereforeavoided and suitably large breakdown voltages are achieved.

SUMMARY

In a first aspect, an IGBT die structure includes an IGBT that has anovel charge carrier injection/extraction structure. The IGBT diestructure includes an N+ type buffer layer that is disposed on a P++type substrate layer. An N− type drift layer is disposed on the N+ typebuffer layer. The N+ type buffer layer and the N− type drift layer areepitaxial layers, whereas the P++ type substrate is of monocrystallinesubstrate material. The upper surface of N− type drift layer is asubstantially planar upper surface of semiconductor material. A P typebody region extends down into the N− type drift layer from thissubstantially planar upper semiconductor surface. An N+ type sourceregion extends down into P type body region. A gate is separated fromthe planar upper semiconductor surface by a thin gate insulation layer.An emitter terminal is coupled to the N+ type source region and to the Ptype body region. A gate terminal is coupled to the gate. A collectorterminal on the bottom side of the IGBT die structure is coupled to theP++ type substrate layer.

In addition to these structures is the novel “charge carrierinjection/extraction structure”. The charge carrier injection/extractionstructure in one example is an auxiliary P type well region and a chargecarrier injection/extraction terminal. The auxiliary P type well regionextends down into the N− type drift layer from the substantially planarupper semiconductor surface much like the P type body region of the IGBTdoes, but the auxiliary P type well region has no N+ type source region.The auxiliary P type well region is separated from the P type bodyregion by an amount of the N− type drift layer. The auxiliary P typewell region is also separated from the underlying P++ type substratelayer by another amount of the N− type drift layer. The charge carrierinjection/extraction terminal is a metal terminal like the otherterminals of the IGBT structure, but the charge carrierinjection/extraction terminal is coupled to the auxiliary P type wellregion and is not coupled to any of the other terminals of the IGBT diestructure.

In one multi-cell implementation, there may be many unit cells in theIGBT die structure. Each unit cell includes its own auxiliary P typewell region. All the auxiliary P type well regions of all the unit cellsare coupled together by metal of the charge carrier injection/extractionterminal.

During a turn on time TON of the IGBT, a current I_(A) can be injectedthrough the charge carrier injection/extraction terminal, through theauxiliary P type well region, and into the N− type drift layer, therebyinjecting charge carriers into the N− type drift layer. The injection ofthese charge carriers accelerates the establishment of electron/hole gasin the N− type drift layer and thereby reduces IGBT turn on time.

During a turn off time TOFF of the IGBT, a current I_(A) can beextracted from the auxiliary P type well region and out of the IGBT diestructure via the charge carrier injection/extraction terminal. Theextraction of this current from the charge carrier injection/extractionterminal causes charge carriers to be removed from the N− type driftlayer. The removal of these charge carriers accelerates the eliminationof the electron/hole gas in the N− type drift layer and thereby reducesIGBT turn off time.

By reducing IGBT turn on time and by reducing IGBT turn off time,associated switching energy losses in a system employing switching IGBTsare reduced. In addition to reducing IGBT turn on time and IGBT turn offtime, a current I_(A) can be injected into the charge carrierinjection/extraction terminal throughout the on time of the IGBT. Thiscontinuous supply of current into the charge carrierinjection/extraction terminal maintains a high density of theelectron/hole gas in the N− type drift layer and reduces V_(CE(SAT)) ofthe IGBT. The reduction in V_(CE(SAT)) during the on time of the IGBTserves to reduce conduction losses.

In a second aspect, an IGBT assembly includes an IGBT die structure anda current injection circuit. In some examples, the IGBT die structureand the current injection circuit are packaged together in asemiconductor device package. In other examples, the IGBT die structureis packaged in a semiconductor device package and the current injectioncircuit is disposed outside the package. The current injection circuitdetects the beginning of a turn on time TON, and in response injects acurrent I_(A) into the charge carrier injection/extraction terminal ofthe IGBT die structure during the turn on time TON. The injection of thecurrent I_(A) reduces the duration of the turn on time TON. In addition,the current injection circuit may detect the beginning of a turn offtime TOFF, and in response may extract a current I_(A) from the chargecarrier injection/extraction terminal of the IGBT die structure. Theextraction of the current I_(A) reduces the duration of the turn offtime TOFF.

There are many ways of realizing the current injection circuit of theIGBT assembly. In one example, the current injection circuit is acurrent transformer. The current transformer may involve a first bondwire and a second bond wire that are magnetically coupled together. Thecurrent transformer may involve a small surface mount transformer. Afirst winding of the small surface mount transformer is wound inclockwise fashion around a core. A second winding of the surface mounttransformer is wound in counter-clockwise fashion around the core. Thesmall surface mount transformer in some cases is mounted directly ontothe emitter terminal of the IGBT die within a semiconductor devicepackage. When an emitter current begins to flow through a first windingof the current transformer at the beginning of a turn on time of theIGBT, the transformer causes an I_(A) current to flow in the secondwinding and into the charge carrier injection/extraction terminal of theIGBT die structure. Likewise, when the emitter current begins to drop atthe beginning of a turn off time of the IGBT, the transformer causes acurrent I_(A) to be drawn from the charge carrier injection/extractionterminal of the IGBT die structure and into the second winding of thetransformer.

Further details and embodiments and techniques are described in thedetailed description below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1 (Prior Art) is a symbol of a prior art N-channel enhancement typeInsulated Gate Bipolar Transistor (IGBT).

FIG. 2 (Prior Art) is a simplified cross-sectional diagram of a priorart IGBT.

FIG. 3 (Prior Art) is a simplified cross-sectional diagram of an oldIGBT structure involving a diverter that was sometimes employed in thepast to prevent latchup.

FIG. 4 is a diagram of a more contemporary IGBT design that is notsusceptible to latchup.

FIG. 5 is a symbol of a novel IGBT die structure that has a chargecarrier injection/extraction terminal.

FIG. 6 is a cross-sectional diagram of a novel IGBT die structure thatincludes a charge carrier injection/extraction structure.

FIG. 7 is a cross-sectional diagram that illustrates how injection of acurrent into the IGBT die structure of FIG. 6 reduces IGBT turn on time.

FIG. 8 is a cross-sectional diagram that illustrates how extraction of acurrent out of the IGBT die structure of FIG. 6 reduces IGBT turn offtime.

FIGS. 9A-14A and 9B-14B are diagrams of various steps in a method ofmanufacturing an Atomic-Lattice-Layer (A-L-L) unit cell of an IGBT diestructure, where the IGBT die structure has a charge carrierinjection/extraction terminal.

FIG. 15 is a top-down diagram of an IGBT die structure of which the unitcell 108 is a part. The diagram shows a two-dimensional array ofauxiliary P type well regions.

FIG. 16 is a top-down diagram of the IGBT die structure of FIG. 15,except that the polysilicon layer that makes up the polysilicon gates ofthe IGBTs is shown.

FIG. 17 is a top-down diagram of the IGBT die structure of FIG. 15,except that the first metal layer (after deposition and patterning) isshown.

FIG. 18 is a top-down diagram of the IGBT die structure of FIG. 15,showing the first metal layer (after deposition and patterning), andalso showing exposed portions of the underlying polysilicon.

FIG. 19 is a top-down diagram of the IGBT die structure of FIG. 15,showing the second metal layer (after deposition and patterning).

FIG. 20 is a top-down diagram of the IGBT die structure of FIG. 15,showing the pad portions 118-120 of the three metal terminals on theupper surface of the IGBT die structure.

FIG. 21 is a diagram of a four-terminal packaged IGBT device inaccordance with one novel aspect.

FIG. 22 is a diagram of the three-terminal packaged IGBT device inaccordance with one novel aspect, where the three-terminal packaged IGBTdevice has a current transformer.

FIGS. 23 and 24 illustrate operation of the current transformer of FIG.22.

FIG. 25 is a perspective diagram of a surface mount current transformer.

FIG. 26 is a cross-sectional view of the surface mount currenttransformer of FIG. 25.

FIG. 27 is a perspective diagram that shows the contents of a packagedIGBT device. The contents include the surface mount current transformerof FIGS. 25 and 26 mounted on the emitter terminal of an IGBT diestructure.

FIG. 28 is a perspective diagram of the packaged IGBT device of FIG. 27.

FIG. 29 is a diagram of an IGBT assembly in accordance with one novelaspect.

FIG. 30 is a waveform diagram that illustrates an operation of the IGBTassembly of FIG. 29 in use in an application of driving an inductiveload.

FIG. 31 is a waveform diagram that illustrates an operation of aconventional IGBT in use in an application of driving the same inductiveload as in the waveforms of FIG. 30.

FIG. 32 is a flowchart of a method of reducing IGBT turn on time inaccordance with one novel aspect.

FIG. 33 is a flowchart of a method of reducing IGBT turn off time inaccordance with one novel aspect.

DETAILED DESCRIPTION

Reference will now be made in detail to background examples and someembodiments of the invention, examples of which are illustrated in theaccompanying drawings. In the description and claims below, when a firstobject is referred to as being disposed “over” or “on” a second object,it is to be understood that the first object can be directly on thesecond object, or an intervening object may be present between the firstand second objects. Similarly, terms such as “upper”, “top”, “up”,“down”, “bottom”, and “backside” are used herein to describe relativeorientations between different parts of the structure being described,and it is to be understood that the overall structure being describedcan actually be oriented in any way in three-dimensional space. Thenotations N+, N−, N, P++, P+, and P are only relative, and are to beconsidered in context, and do not denote any particular dopantconcentration range. A region denoted generally in the claims to be “Ptype”, however, is being indicated to be P type doped, and may belightly doped, moderately doped, or heavily doped with P type dopants.Similarly, a region denoted in the claims to be N type is beingindicated to be N type doped, and may be lightly doped, moderatelydoped, or heavily doped with N type dopants.

FIG. 5 is a symbol 50 of an N-channel enhancement type Insulated GateBipolar Transistor (IGBT) that has a “charge carrierinjection/extraction terminal” in accordance with one novel aspect. IGBTsymbol 50 has a gate terminal (G) 51, an emitter terminal (E) 52, acollector terminal (C) 53, and a charge carrier injection/extractionterminal (A) 54. The charge carrier injection/extraction terminal isalso referred to in this patent document as the “auxiliary terminal” (A)54 or the “auxiliary P type well terminal” (A) 54.

FIG. 6 is a cross-sectional diagram of an IGBT die structure 55. IGBTdie structure 55 includes a vertical IGBT that has a novel chargecarrier injection/extraction structure 56. Epitaxial layers 57 and 58are grown on a P++ type semiconductor substrate layer 59. Epitaxial N+type buffer layer 57 is disposed on the P++ type substrate layer 59.Epitaxial N− type drift layer 58 is disposed on the N+ type buffer layer57. The upper surface of N− type drift layer 58 is a substantiallyplanar upper surface of semiconductor material. A P type body region 59extends down into the N− type drift layer 58 from this substantiallyplanar upper semiconductor surface. An N+ type source region 60 extendsdown into P body region 59 from the substantially planar uppersemiconductor surface. A gate 61, such as a gate of polysiliconmaterial, is separated from the planar upper semiconductor surface by athin gate insulation layer 62. Reference number 63 represents a gatemetal terminal (G) (not shown) that allows connection to the gate 61. Anemitter metal terminal (E) 64 straps each P type body region 59 to itscorresponding N+ type source region 60 as shown. A collector metalterminal (C) 65 is disposed on the bottom side of P++ type substratelayer 59. Charge carrier injection/extraction structure 56 includes anauxiliary P type well region 66 and a charge carrierinjection/extraction metal terminal (A) 67. As mentioned above, thecharge carrier injection/extraction terminal 67 is also referred to asthe auxiliary terminal of the device. Auxiliary P type well region 66extends down into the N− type drift layer 58 from the substantiallyplanar upper semiconductor surface.

Charge carrier injection/extraction terminal 67 is a separate metalterminal that is not electrically connected to emitter terminal 64, noris it connected to any other terminal of the IGBT die structure. Thevoltage between emitter terminal 64 and terminal 67 on the auxiliary Ptype well region 66 is not clamped by any diode as in a diode diverterstructure. There is no N+ region extending down into the auxiliary Ptype well region 66 from the upper surface of the semiconductormaterial. The auxiliary P type well region is not a floating P well thatis not connected to other terminals of the IGBT, but rather theauxiliary P type well region is connected to charge carrierinjection/extraction terminal 67 as shown in FIG. 6.

A simplified explanation of device operation is set forth below. Duringturn on of the IGBT, electrons flow from N+ type source region 60,leftward through a thin conductive channel region under the gate andlaterally across the P type body region 59, to the portion of the N−type drift layer 58 under gate 61, and then downward through N-typedrift layer 58, and downward through N+ type buffer layer 57. Thiscurrent flow passes through P++ type substrate layer 59 and to collectorterminal 65. The flow of electrons into the N− type drift layer 58causes an increase in electron density in the N-type drift layer 58.This increase in electron density causes the potential of the N− typedrift layer 58 to decrease, thereby forward biasing the PN junctionbetween the P++ type substrate layer 59 and the N+ type buffer layer 57.The forward biasing of this junction causes holes to be emitted from P++emitter layer 59 into N+ buffer layer 57. Some of the holes recombinewith electrons in the N− type drift layer 58, but others of the injectedholes pass upward through the N− type drift layer 58, into the P typebody region 59, under N+ type source region 60, and to the emitterterminal 64. Due to the injection of holes, the concentration of holesin the N-type drift layer 58 increases. This increase in holeconcentration in turn draws more electrons from the N+ type sourceregion 60, through the conductive channel, and into the N− type driftlayer 58. The holes are drawn in order to neutralize charge (createcharge neutrality) in the N− type drift layer 58. With holes beinginjected into the N-type drift layer 58 from the P++ type substratelayer 59, and with electrons being drawn into the N− type drift layer 58from the N+ type source region 60 to create charge neutrality, a highdensity electron/hole “gas” is established in the N− type drift layer58. The amount of time required for the IGBT to turn on is limited bythe time required to establish this electron/hole gas.

FIG. 7 illustrates a novel aspect of the IGBT die structure 55 and itsoperation. To reduce the turn on time of the IGBT, a current I_(A) isinjected through the charge carrier injection/extraction terminal 67during the turn on time of the IGBT. Initially, when the channel iscreated under the gate 61, electrons flow from the N+ type source region60, across the channel, and into the N-type drift layer 58. Theelectrons that do not recombine with holes in the N− type drift layer 58pass downward to the collector as explained above. As a result, holesare injected into the N− type drift layer 58. The holes that do notrecombine with electrons in the N− type drift layer 58 pass upward andthrough the P type body region 59 and to the emitter terminal 64 asdescribed above. In a novel aspect, when this emitter current starts toflow, a proportional auxiliary current I_(A) is made to flow into theauxiliary terminal 67. As a result, holes are injected from theauxiliary P type well region 66 and into the adjacent region 68 of theN− type drift layer 58. This serves to increase the hole concentrationin this region 68 of the N-type drift layer 58, and therefore reducesthe time required for holes from other sources to create the highdensity of holes of the electron/hole gas that is to be created in theother areas of the N− type drift layer 58. Because the volume of N-typedrift layer 58 that must be filled with holes from other sources (suchas the P++ substrate layer 59) is decreased, the total time required toachieve the high density of holes of the “gas” throughout the entire N−type drift layer 58 is also reduced.

In addition, the injection of holes into the N-type drift layer 58 dueto the I_(A) current flow causes more electrons to be drawn from the N+type source region 60 and across the channel region, into the N− typedrift layer 58, and into region 68. This increased flow of electrons isto equalize charge (create charge neutrality) in region 68. Chargeneutrality is not actually achieved, but the flow of electrons partiallyequalizes charges in this region. The overall flow of electrons from theN+ type source region 60 into the N− type drift layer 58 is higher thanit would be otherwise without the injection of holes into region 68 fromauxiliary P type well region 66. Due to the increased flow of electronsfrom the N+ type source region 60, the overall amount of time requiredto establish the high electron concentration of the “gas” everywhere inthe N− type drift layer 58 is also reduced.

In addition to reducing the turn on time of the IGBT, the injected I_(A)current also reduces the collector-to-emitter saturation voltageV_(CE(SAT)) during the IGBT's static on time. The extra holes andelectrons flowing into the N-type drift layer 58 as a result of theauxiliary terminal 67 cause a higher density of electrons and a higherdensity of holes to exist in the N− type drift layer 58 than wouldotherwise exist were there no auxiliary P type well region 66. Thehigher densities of holes and electrons manifest themselves as a lowerresistance between the collector and emitter when the IGBT is on. Inoperation of the IGBT, this lower collector-to-emitter resistanceresults in a correspondingly lower V_(CE(SAT)).

In order to turn off the IGBT, the flow of electrons from the N+ typesource region 60 is stopped under control of the gate due to the channelregion being removed. The gate-to-emitter voltage V_(GE) may, forexample, be dropped from 15 volts to zero volts so that the channel isremoved. With no conductive channel through which electrons can flow,the flow of electrons from emitter terminal 64 is turned off fairlyrapidly. The injection of holes from the P++ type substrate layer 59 isalso suspended fairly rapidly due to the potential of the N− type driftlayer rising and reverse biasing the P++ substrate to N+ type bufferjunction. But even without holes and electrons flowing into the N− typedrift layer 58, there still remain holes and electrons of the highdensity gas that are now trapped in the N− type drift layer 58. Thesetrapped electrons and holes must either recombine or be removed for theIGBT to be off. In a conventional IGBT structure, a substantial “tail”of current continues to flow through the IGBT as the IGBT turns off dueto the removal of the one of these trapped charges that do notrecombine. Time is required for the high density of holes and electronsin the N− type drift layer 58 to recombine, or for the electrons andholes to otherwise escape from the N− type drift layer 58, before thehigh density electron/hole “gas” is gone and the IGBT is off.

FIG. 8 illustrates a novel aspect of the IGBT structure and operation.To reduce the turn off time of the IGBT, a current I_(A) is extractedthrough the charge carrier injection/extraction terminal 67 during theturn off time of the IGBT. Due to the I_(A) current being extracted,holes are drawn from region 69 and into the auxiliary P type well region66. Rather than having to wait for recombination or other mechanisms toreduce hole concentration in this region 69, the hole concentration isreduced by the current I_(A) being withdrawn from the auxiliary terminal67. Reducing the concentration of holes in region 69 by use of theauxiliary terminal 67 reduces the number of holes that have to beremoved from the other parts of the N− type drift layer 58 byrecombination or by flow through the P type body region 59 to theemitter terminal. As a result, the amount of time for the high densityof holes of the “gas” to be removed from the entire N− type drift layer58 is reduced.

In addition, the flow of holes out of region 69 through the auxiliaryterminal 67 causes a depletion region and corresponding electric fieldat the auxiliary P type well region 66 to N− type drift layer 58boundary. This electric field serves to sweep electrons away from theboundary and deeper into the N− type drift layer 58. The flow of theseelectrons that are pushed away from the boundary is illustrated witharrows 70. Rather than having to wait for the high density of electronsto be removed from region 69 by recombination or by other mechanisms,the electrons in region 69 are pushed out by the electric field as aresult of the current I_(A). Reducing the concentration of electrons inregion 69 in this way reduces the number of electrons of the gas thathave to be removed from the other parts of the N− type drift layer 58 byrecombination or by flow out of the collector. As a result, the totaltime required to remove the high density electron/holes gas from the N−type drift layer 58 is reduced as compared to what that time would bewere there to be no auxiliary P type well region 66.

During a normal operation of the IGBT, the IGBT is turned on during aturn on time, then the IGBT is operated in the forward conduction modefor a period of time, then the IGBT is turned off during a turn offtime, and then the IGBT is operated in the forward block mode. Thiscycle typically repeats, over and over. During the turn on time, anauxiliary current I_(A) is injected into the auxiliary terminal 67thereby reducing turn on time. During forward conduction mode operation,the current I_(A) is also injected into the auxiliary terminal 67 toreduce V_(CE(SAT)). During the turn off time, an auxiliary current I_(A)is drawn out of the auxiliary terminal 67 in order to reduce turn offtime. Reducing turn on time, reducing turn off time, and reducingV_(CE(SAT)) in this way reduces conduction losses in the IGBT.

FIGS. 9A-14A and 9B-14B are diagrams of various steps in the manufactureof an Atomic-Lattice-Layer (A-L-L) unit cell 108 of an IGBT die.

FIG. 9A is a top-down diagram of unit cell 108. Unit cell 108 is asquare when viewed from this perspective. FIG. 9B is a cross-sectionalview taken along line A-A in FIG. 9A. There is a centrally locatedauxiliary P type well region 100 surrounded by a P type body region 101.The auxiliary P type well region 100 and the P type body region 101extend down into an N− type drift layer 102. N-type drift layer 102 isdisposed on an N+ type buffer layer 103. Layers 102 and 103 areepitaxial layers that are disposed on a P++ type substrate layer 104.Extending into the P type body region 101 from the upper surface of thesemiconductor material is an N+ type source region 105. A polysilicongate 106 is separated from the underlying semiconductor material by athin gate insulating layer 107.

FIG. 10A is a top-down diagram of the unit cell 108 after the step offorming the polysilicon gate has been completed, but in the diagram ofFIG. 10A the polysilicon layer is not shown so that the boundaries ofthe auxiliary P type well region 100 and the boundaries of the P typebody region 101 will be evident. FIG. 10B is a cross-sectional viewtaken along line A-A in FIG. 10A.

FIG. 11A is a top-down diagram of unit cell 108 after the step ofdepositing and patterning a layer of oxide insulation 109 over the gate106. FIG. 11B is a cross-sectional view taken along line A-A in FIG.11A.

FIG. 12A is a top-down diagram of the unit cell 108 after the step ofdepositing and patterning a first metal layer into a feature 110 of theauxiliary terminal (metal that extends down to the auxiliary P type wellregion 100) and a feature 111 of an emitter terminal (metal that extendsdown to the N+ type source region 105 and P− type body region 101). FIG.12B is a cross-sectional view taken along line A-A in FIG. 12A.

FIG. 13A is a top-down diagram of the unit cell 108 after the step ofdepositing and forming a second layer of insulation 112. FIG. 13B is across-sectional view taken along line A-A in FIG. 13A.

FIG. 14A is a top-down diagram of the unit cell 108 after the step ofdepositing and forming a second metal layer into a second feature 113 ofthe emitter terminal.

FIG. 15 is a top-down diagram of an IGBT die 114 of which the unit cell108 is a part. The locations of the auxiliary P type well regions areshown in FIG. 15. The auxiliary P type well regions are arranged in atwo-dimensional array of rows and columns as shown.

FIG. 16 is a top-down diagram of IGBT die 114 showing the polysiliconlayer 115 that makes up the polysilicon gates of the IGBTs of thestructure, including the polysilicon gate 106 of unit cell 108.

FIG. 17 is a top-down diagram of IGBT die 114 showing the first metallayer after deposition and patterning. The first metal layer forms metal110 (that extends down to the auxiliary P type well regions) and metal111 (that extends down to the N+ type source regions and the P type bodyregions). The first metal layer also forms the gate pad and bus line115.

FIG. 18 is a top-down diagram of IGBT die 114 showing the polysiliconlayer underneath the patterned first metal layer.

FIG. 19 is a top-down diagram of IGBT die 114 showing the second metallayer. The second metal layer is deposited and patterned to form afeature 113 of the emitter terminal, a feature 116 of the auxiliary Pwell terminal, and a feature 117 of the gate terminal. Metal features113, 116 and 117 are parts of the upper surface of the die (ignoring anyoverlying passivation layers).

FIG. 20 is a top-down diagram of IGBT die 114 showing the pad portion118 of the emitter metal terminal, the pad portion 119 of the auxiliaryP type well metal terminal, and the pad portion 120 of the gate metalterminal. Pads 118-120 are disposed on the upper surface of the die. Thebackside of the die is covered in metal as well, and that backside metalis the collector metal terminal (not shown) of the IGBT.

FIG. 21 is a diagram of a four-terminal packaged IGBT device 121 inaccordance with one novel aspect. Packaged IGBT device 121 has a gatelead or terminal 122, an auxiliary P type well lead or terminal 123, anemitter lead or terminal 124, and a collector lead or terminal 125. TheIGBT die 114 is of the same construction as shown and explained above inconnection with the prior diagrams. The collector metal on the backsideof IGBT die 114 is mounted to the die attach slug 127 from which thecollector lead 125 extends. The gate pad, the auxiliary P well pad, andthe emitter pad are connected their respective leads 122, 123 and 124 bycorresponding bond wires as shown. Dashed line 128 represents an amountof encapsulant such as an injection molded epoxy resin encapsulant.

FIG. 22 is a diagram of a three-terminal packaged IGBT device 129 inaccordance with another novel aspect. Packaged IGBT device 129 has anemitter transformer lead or terminal (ET) 130, a gate lead or terminal(G) 131, and a collector lead or terminal (C) 132. The IGBT die 114 isof the same construction as shown and explained above in connection withthe prior diagrams except that the auxiliary P well pad, the gate pad,and the emitter pad on the IGBT upper surface are arranged differently.The collector metal on the backside of IGBT die 114 is mounted to thedie attach slug 133 from which the collector lead 132 extends. The gatepad G is connected by a bond wire to gate lead 131 as shown. Theauxiliary P type well pad A is connected by a bond wire 134 to a distantpart of the emitter terminal metal, and the emitter transformer lead(ET) 130 is connected by a bond wire 135 to a distant part of theemitter terminal metal E, so that the two wires 134 and 135 extend pasteach other in parallel fashion as shown. A drop 136 of resin thatincludes suspended particles of a magnetic material such asferromagnetic particles is disposed on the emitter metal. The bond wires134 and 135 extend through this drop 136 as shown. The drop 136functions to increase the magnetic coupling between bond wires 134 and135. Bond wires 134 and 135 together with drop 136 form a currenttransformer. Dashed line 137 represents an amount encapsulant such as anamount of injection molded epoxy resin encapsulant.

FIGS. 23 and 24 illustrate operation of the current transformer of FIG.22. As shown in FIG. 23, when an emitter transformer current I_(ET)starts to flow out of the emitter pad of the IGBT die, the emittertransformer current I_(ET) passes through bond wire 135 on its way toemitter transformer lead (ET) 130 of the package. This current flowI_(ET) causes energy to be stored in the magnetic core. The magneticcore in this case involves the drop 136 of ferromagnetic particles. Thebond wire 135 is, however, magnetically coupled to bond wire 134.Accordingly, as shown in FIG. 24, the magnetic coupling causes anauxiliary current I_(A) to flow from the emitter pad, through thetransformer, and into the auxiliary pad A of the IGBT die. As a resultof the conduction of the auxiliary current I_(A), the magnetic core isleft with less flux and stores less energy. Due to operation of thiscurrent transformer, the increase in emitter current I_(E) during theturn on time of the IGBT causes an auxiliary current I_(A) to beinjected into the auxiliary P type well terminal A of the IGBT, and thisinjection of current reduces IGBT turn on time as explained above.Similarly, due to operation of this current transformer, the decrease inemitter current I_(E) during the turn off time of the IGBT causes anauxiliary current I_(A) to be extracted out of the auxiliary P type wellterminal of the IGBT, and this extraction of current reduces IGBT turnoff time as explained above. The actual emitter current I_(E) flows fromthe emitter terminal metal and into the semiconductor material of theIGBT die structure. There is a current branch in the emitter terminalmetal of the device in that the I_(ET) current comes into the emittermetal terminal, and currents I_(E) and I_(A) come out of the currentbranch.

FIG. 25 is a perspective diagram of another embodiment of a currenttransformer 140 usable to inject I_(A) current into, and to extractI_(A) current out of, the auxiliary P type well terminal of an IGBT.

FIG. 26 is a cross-sectional diagram of the current transformer 140 ofFIG. 25. A first winding 141 extends from metal terminal 142, is woundaround the ferrite core 143 in clockwise fashion, and terminates atmetal terminal 146. A second winding 145 extends from metal terminal142, is wound around the ferrite core 143 in counter-clockwise fashion,and terminates at metal terminal 144. The turns ratio of transformer 140is 1:1.

FIG. 27 is a perspective diagram of a use of the current transformer 140in combination with IGBT die 114 and an anti-parallel diode 147. TheIGBT die 114 is of the same construction as shown and explained above inconnection with the prior diagrams. The collector metal (not shown) onthe backside of the IGBT die 114 is surface-mounted to the die attachslug 148 from which the collector lead (C) 149 extends. The metalterminal 142 on the bottom side of the current transformer 140 issurface-mount connected to the upper surface of the emitter metal pad onthe upper surface of IGBT die 114. An emitter current flowing out of theemitter pad of the IGBT die 114 passes up through the metal terminal 142of the current transformer 140, through the clockwise winding 141,through metal terminal 146, through a bond wire 150, and to the emittertransformer lead (ET) 151 of the package. This flow of I_(ET) currentcauses an auxiliary P well current I_(A) to flow from the metal terminal142 of the current transformer 140, through counter-clockwise winding145, through metal terminal 144, through a bond wire 152, and into theauxiliary P type well pad (A) 119 of IGBT die 114. The gate pad (G) 120of IGBT die 114 is connected by a bond wire 153 to the gate lead (G) 154of the package. A bond wire 155 connects the emitter transformer lead(ET) 151 to the anode wire bond pad 156 of anti-parallel diode 147. Thecathode electrode (not shown) on the backside of the anti-parallel diode147 is surface mounted to the die attach slug 148 and therefore is alsoconnected to the collector (not shown) on the backside of the IGBT die114. The entire assembly is encapsulated in an amount of an encapsulantsuch as an injection molded epoxy resin encapsulant 157.

FIG. 28 is a perspective view of the three-terminal packaged device ofFIG. 27. The amount of encapsulant 157 overmolds the componentsillustrated in FIG. 27.

FIG. 29 is a schematic diagram of an IGBT assembly 160 having circuitryfor injection/extracting current into/from an auxiliary P well. IGBTassembly 160 includes IGBT die 114 and a current injection/extractioncircuit 161. There are many suitable ways of making the currentinjection/extraction circuit 161. The function of the currentinjection/extraction circuit 161 is to inject an auxiliary current I_(A)into the auxiliary P type well terminal 67 of the IGBT die structure 55during a turn on time TON of the IGBT, and to extract an auxiliarycurrent I_(A) out of the auxiliary P type well terminal 67 of the IGBTdie structure 55 during a turn off time TOFF of the IGBT. For example,circuit 161 may detect V_(GE) starting to transition high, and after asmall delay may inject a current I_(A) into the auxiliary P type wellterminal 67. Circuit 161 may detect V_(GE) starting to transition low,and after a small delay may extract a current I_(A) from the auxiliary Ptype well terminal 67. In addition, circuit 161 may supply a currentI_(A) into the auxiliary P type well terminal 67 in a static waythroughout times when the IGBT is on and conductive.

In one example, circuit 161 is realized as the current transformer ofFIGS. 25 and 26. In another example, circuit 161 is realized as thebondwire/resin drop current transformer structure of FIG. 22. In caseswhere circuit 161 is a transformer, the IGBT may be used as a switch andthe switching frequency is set to be high enough that I_(A) does notdecay to zero before the next switching cycle starts again. The circuit161 need not, however, necessarily involve a current transformer. Ratherthe circuit 161 may sense the turn on time and the turn off time, andinject or extract I_(A) current as appropriate using other circuitry solong as the current injection/extraction function is achieved. In somecases, circuit 161 performs only the current injection function toaccelerate turn on time. In other cases, circuit 161 performs only thecurrent extraction function to accelerate turn off time. Circuit 161 maybe implemented as part of a packaged IGBT device. Alternatively, circuit161 may be disposed outside the package that houses the IGBT device.

FIG. 30 is a waveform diagram that illustrates operation of the IGBT diestructure 55 and circuit 161 of FIG. 29 in an application of driving aninductive load at 20 kHz with a sixty percent duty cycle. Immediatelyprior to time T1, the IGBT is off. The collector current I_(C) istherefore zero and the emitter current I_(E) is zero. Then at time T1the IGBT is to be turned on. The voltage on the gate V_(GE) is thereforemade to rise. As a result of the conduction mechanisms described abovein connection with FIG. 7, the collector and emitter currents rise asshown. Due to operation of the current transformer, the change inemitter current I_(E) is about double the change in the auxiliary P wellcurrent I_(A) that is injected into the auxiliary P type well terminal.The “turn on time” TON is defined here as the time between the time whenthe voltage V_(GE) on the gate starts to rise and the time when thecollector-to-emitter voltage V_(CE) has dropped to within ten percent ofits final value. In the example of FIG. 30, V_(CE) starts at +300 voltsat time T1. Its final value is about 2 volts (V_(CE(SAT))). As a resultof the IGBT turning on V_(CE) drops to ten percent of +300 volts (+30volts) by time T2. The time between T1 and T2 is the turn on time TON.

After time T2, the IGBT operates in its forward conduction mode untiltime T3. At time T3, the IGBT is to be turned off. The voltage V_(GE) onthe gate is therefore made to fall, and this causes the IGBT to turn offby the mechanisms described above in connection with FIG. 8. Thecollector and emitter currents therefore decrease in magnitude. Due tooperation of the current transformer, the amount of current I_(A)extracted from the auxiliary P well terminal is about double thedecrease in the emitter current I_(E). The turn off time TOFF is definedhere as the time between the time when the voltage V_(GE) on the gatestarts to decrease and the time when the collector current I_(C) hasdropped to within ten percent of its final value. In the example of FIG.30, I_(C) starts at ten amperes and its final value is zero amperes.Time T4 is the time when the collector current I_(C) has dropped to oneampere. The turn off time TOFF is therefore the time between times T3and T4.

After time T4, the IGBT operates in its forward blocking mode and isoff. The IGBT stays off until time T5, when the cycle repeats and V_(GE)is increased to turn on the IGBT once more. The size of the currenttransformer and the frequency of switching are such that the auxiliarycurrent I_(A) does not drop below zero volts at any time between T1 andT3 when the IGBT is to be on. If I_(A) were allowed to drop below zerovolts during this time, then the auxiliary P type well region wouldfunction like a diverter and the V_(CE(SAT)) of the IGBT would beincreased in an undesirable manner leading to increased conductionlosses.

FIG. 31 is a waveform diagram of an IGBT of similar construction to theIGBT die structure 55 of FIG. 29 driving the same inductive load, exceptthat the IGBT whose operation is depicted in FIG. 31 has no auxiliary Ptype well region and has no current transformer or circuit 161 injectingor extracting any I_(A) current to/from the IGBT. The turn on time TONin FIG. 31 is longer than the turn on time TON in FIG. 30. The longerturn on time TON is due to more time being required to establish theelectron/hole gas in the N− drift layer of the IGBT than is required inthe novel IGBT die structure 55. The turn off time TOFF in FIG. 31 isalso longer than the turn off time TOFF in FIG. 30. The longer turn offtime TOFF is due to more time being required to remove electrons andholes of electron/hole gas from the N− drift layer of the IGBT than isrequired in the novel IGBT die structure 55.

FIG. 32 is a flowchart of a method 200 in accordance with one novelaspect. The turn on time TON of an IGBT is reduced by injecting (step201) charge carriers from an auxiliary P type well region of the IGBTinto an N− type drift layer of the IGBT during a turn on time of theIGBT. In one example of the method 200, the IGBT is the IGBT of IGBT diestructure 55 of FIG. 6, the auxiliary P type well region is theauxiliary P type well region 66 of the IGBT die structure 55 of FIG. 6,and the N− type drift layer is the N− type drift layer 58 of the IGBTdie structure 55 of FIG. 6.

FIG. 33 is a flowchart of a method 300 in accordance with one novelaspect. The turn off time TOFF of an IGBT is reduced by extracting (step301) charge carriers from an N− type drift layer of the IGBT into anauxiliary P type well region of the IGBT during a turn off time of theIGBT. In one example of method 300, the IGBT is the IGBT of IGBT diestructure 55 of FIG. 6, the auxiliary P type well region is theauxiliary P type well region 66 of the IGBT die structure 55 of FIG. 6,and the N− type drift layer is the N− type drift layer 58 of the IGBTdie structure 55 of FIG. 6.

Although certain specific embodiments are described above forinstructional purposes, the teachings of this patent document havegeneral applicability and are not limited to the specific embodimentsdescribed above. The disclosed auxiliary P type region and associatedterminal that injects/extracts charge carriers into/from an IGBT driftlayer is not limited to use in a vertical IGBT structure, but ratherapplies generally to any IGBT structure or topology. Accordingly,various modifications, adaptations, and combinations of various featuresof the described embodiments can be practiced without departing from thescope of the invention as set forth in the claims.

What is claimed is:
 1. An Insulated Gate Bipolar Transistor (IGBT)assembly comprising: an IGBT die structure having a first terminal, asecond terminal, a third terminal, and a fourth terminal, wherein thefirst terminal is coupled to an emitter of an IGBT, wherein the secondterminal is coupled to a gate of the IGBT, wherein the third terminal iscoupled to an auxiliary P type well region of the IGBT, and wherein thefourth terminal is coupled to a collector of the IGBT; and a currentinjection circuit having a first terminal, a first bond wire, a secondbond wire and a ferromagnetic material, wherein the first terminal ofthe current injection circuit is coupled to the third terminal of theIGBT die structure and wherein the first bond wire and the second bondwire are magnetically coupled together by the ferromagnetic material. 2.The IGBT assembly of claim 1, wherein the current injection circuitinjects a current into the third terminal of the IGBT die structureduring a turn on time TON of the IGBT.
 3. The IGBT assembly of claim 1,wherein the current injection circuit injects a current into the thirdterminal of the IGBT die structure during a turn on time TON of theIGBT, and wherein the current injection circuit extracts a current outof the third terminal of the IGBT die structure during a turn off timeTOFF of the IGBT.
 4. The IGBT assembly of claim 3, wherein the firstbond wire and the second bond wire form a current transformer.
 5. TheIGBT assembly of claim 3, wherein the third terminal is directlyconnected to the auxiliary P type well region of the IGBT die structure,and wherein the third terminal is not directly connected to any N typesemiconductor material of the IGBT die structure.
 6. The IGBT assemblyof claim 1, wherein the current injection circuit has a second terminalcoupled to the first terminal of the IGBT die structure.
 7. The IGBTassembly of claim 1, further comprising: an emitter lead, wherein thefirst bond wire connects the first terminal of the current injectioncircuit to the third terminal of the IGBT die structure, and wherein thesecond bond wire connects a second terminal of the current injectioncircuit to the emitter lead.
 8. The IGBT assembly of claim 1, furthercomprising: a semiconductor device package, wherein the IGBT diestructure and the current injection circuit are disposed within thesemiconductor device package.
 9. The IGBT assembly of claim 1, furthercomprising: a semiconductor device package, wherein the IGBT diestructure is disposed within the semiconductor device package, andwherein the current injection circuit is disposed outside thesemiconductor device package.
 10. The IGBT assembly of claim 1, whereinthe IGBT die structure and the current injection circuit are packagedtogether in a semiconductor device package, and wherein the first andsecond bond wires are magnetically coupled together within thesemiconductor device package.
 11. The IGBT assembly of claim 1, whereinparticles of the ferromagnetic material are suspended in a resin, andwherein the first bond wire and the second bond wire extend through theresin.
 12. The IGBT assembly of claim 1, wherein the IGBT die structureand the current injection circuit are packaged together in asemiconductor device package, wherein the current injection circuit is atransformer having a first winding that is wound in a clockwisedirection around a core, and having a second winding that is wound in acounterclockwise direction around the core.
 13. The IGBT assembly ofclaim 1, wherein IGBT die structure and the current injection circuitare packaged together in a semiconductor device package, wherein thecurrent injection circuit is a transformer, and wherein a terminal ofthe transformer is directly bonded to the first terminal of the IGBT diestructure.
 14. A method comprising: providing an Insulated Gate BipolarTransistor (IGBT) die structure and a current injection circuit togetherin a semiconductor device package, wherein the IGBT die structure has afirst terminal, a second terminal, a third terminal, and a fourthterminal, wherein the third terminal is coupled to an auxiliary P typewell region, wherein the current injection circuit has a first bondwire, a second bond wire and a ferromagnetic material, wherein the firstbond wire and the second bond wire are magnetically coupled together bythe ferromagnetic material, and wherein the current injection circuit iscoupled so that it can inject a current into the third terminal.
 15. Themethod of claim 14, wherein the current injection circuit is a currenttransformer.
 16. The method of claim 14, wherein the first and secondbond wires are coupled together within the semiconductor device package.17. The method of claim 14, wherein the first bond wire forms a firstwinding, wherein the second bond wire forms a second winding, whereinthe first winding is wound in a clockwise direction around theferromagnetic material, and wherein the second winding is wound in acounterclockwise direction around the ferromagnetic material.
 18. Amethod comprising: injecting a current from a current injection circuitand into a third terminal of an Insulated Gate Bipolar Transistor (IGBT)die structure during a turn on time TON of an IGBT, wherein the thirdterminal of the IGBT die structure is coupled to an auxiliary P typewell region of the IGBT, wherein the IGBT die structure also has a firstterminal, a second terminal, and a fourth terminal, wherein the currentinjection circuit has a first winding and a second winding that aremagnetically coupled together by a ferromagnetic material, and whereinthe third terminal of the IGBT is connected to the first winding; andextracting a current from the third terminal of the IGBT die structureand into the current injection circuit during a turn off time TOFF ofthe IGBT, wherein the current injection circuit and the IGBT diestructure are parts of an IGBT assembly.
 19. The method of claim 18,wherein the IGBT assembly comprises a semiconductor device package, andwherein the IGBT die structure and the current injection circuit aredisposed within the semiconductor device package.
 20. The method ofclaim 18, wherein the IGBT assembly comprises a semiconductor devicepackage, wherein the IGBT die structure is disposed within thesemiconductor device package, and wherein the current injection circuitis disposed outside the semiconductor device package.
 21. An InsulatedGate Bipolar Transistor (IGBT) assembly comprising: an IGBT diestructure having a first terminal, a second terminal, a third terminal,and a fourth terminal, wherein the first terminal is coupled to anemitter of an IGBT, wherein the second terminal is coupled to a gate ofthe IGBT, and wherein the fourth terminal is coupled to a collector ofthe IGBT; and means for injecting charge carriers into a drift region ofthe IGBT during a turn on time TON of the IGBT by conducting a currentfrom a first winding, through the third terminal to an auxiliary P wellregion of the IGBT die structure, wherein the first winding ismagnetically coupled to a second winding.
 22. The IGBT assembly of claim21, further comprising: a semiconductor device package having a firstpackage terminal, a second package terminal and a third packageterminal, wherein the first package terminal is coupled to the means,wherein the second package terminal is coupled to the second terminal ofthe IGBT die structure, and wherein the third package terminal iscoupled to the fourth terminal of the IGBT die structure.
 23. The IGBTassembly of claim 21, wherein the means is also for extracting chargecarriers from the drift region of the IGBT during a turn off time TOFFof the IGBT.
 24. The IGBT assembly of claim 21, wherein the meanscomprises a current transformer.
 25. The IGBT assembly of claim 21,wherein the winding is formed from a bond wire connected to the thirdterminal.
 26. The IGBT assembly of claim 21, wherein the means detectsthat the turn on time has started, and in response to the detectingcauses the current to be conducted through the third terminal therebyaccelerating an increase in a concentration of charge carriers in thedrift layer of the IGBT.